The present invention relates to the field of multimedia media content delivery.
For multimedia content delivery, media presentation description (MPD) of dynamic adaptive streaming over hypertext transfer protocol (HTTP) (Dynamic Adaptive Streaming over HTTP or DASH) can be used, specified in 3rd Generation Partnership Project (3GPP) technical specification (TS) 26.247, which appeared earlier as part of the Packet-Switched Streaming (PSS) service, 3GPP TS 26.234.
In order to deliver files over the internet, also the File Delivery over Unidirectional Transport (FLUTE) [Request for Comments (RFC) 3926] can be used. FLUTE is a protocol for unidirectional delivery of files over the Internet. The specification builds on Asynchronous Layered Coding (ALC) [RFC 3450], the base protocol designed for massively scalable multicast distribution.
For serving large groups with the same media content, the Multimedia Broadcast Multicast Service (MBMS) can be employed. The MBMS Download Delivery Method is designed to deliver an arbitrary number of objects via MBMS to a large receiver population. Two delivery methods are defined in MBMS, 3GPP TS 26.346, namely download and streaming.
MBMS download delivery method uses the FLUTE protocol [RFC 3926] when delivering media content over MBMS bearers.
DASH as defined in 3GPP TS 26.247 specifies formats and methods that enable the delivery of streaming service(s) from standard HTTP servers to DASH client(s). It involves the description of a collection of media segments and auxiliary metadata (all referenced by HTTP-uniform resource locators (URLs)) through a MPD.
The download delivery method, i.e. MBMS, allows the delivery of DASH segments and MPDs as defined in 3GPP TS 26.247. Segment URLs are described using FLUTE.
The network may announce the usage of MBMS download delivery method for providing the Media Segments for DASH through the MBMS User Service Description. In such an event, the MBMS User Service Description fragment shall include a MPD element. This element contains a reference to a MPD metadata fragment as defined in 3GPP TS 26.247. Consequently, the User Equipment (UE) can expect that the files provided with the MBMS download delivery method are formatted according to the 3GP file format for DASH as specified in 3GPP TS 26.244. Furthermore, the MPD fragment may contain reference(s) to Initialisation Segment Description fragment(s) as defined in 3GPP TS 26.247.
In order to start consuming a DASH service delivered over MBMS, an MBMS client has to perform the following steps:
Receive the User Service Bundle Description.
Map the MPD to the corresponding Delivery Method.
Set-up the reception of MBMS user service data.
Receive File Delivery Table (FDT) instance from ALC/layered coding transport (LCT) session.
Map the URL of the chosen representation to the Transport Object Identifier (TOI) using received FDT instance.
Store the received object in the UE cache, which can be fetching by DASH client using GET request.
In the process of initializing DASH media content reception transmitted over MBMS a reception of the FDT instance introduces delay which negatively impacts the quality of experience. Before any segment (‘object’) of the chosen representation is received from the MBMS session, an FDT instance must first be received. An FDT instance is transmitted periodically over the ALC/LCT session. The introduced delay depends on the time interval the FDT instance is sent on.
Delivering DASH media content over MBMS for devices that support MBMS reception may be performed by operating a FLUTE client in one of the supported modes. The FLUTE client supports 2 operation modes:
Download-all mode: in this mode the FLUTE client is instructed to download all files (transport objects) in the session, or
Request-based mode: in this mode the FLUTE client is instructed about which files the FLUTE client should download.
However, by the time the DASH client sends the request for a media segment, it might be already being transmitted over the FLUTE session (ALC/LCT session) or the transmission might be already over. This can cause additional delays to enable the FLUTE client to recover the file.
On the other hand, the Download-all mode may not be appropriate in all scenarios as the FLUTE client will download all file sent over the session and this would lead to excessive storage usage, especially when multiple representations are transmitted simultaneously over the same MBMS session.